VCR – Vegetable Crop Report – July 18, 2025

Welcome back to the next VCR of 2025!

Currently most counties are trending slightly above their 10 year average GDD, with Sudbury, Thunder Bay, and Timiskaming county trending slightly below their 10 year average.

Crop Updates

Beans – ozone injury often occurs in the new growth after a period of hot weather and poor air quality. Leaves develop bronze-coloured speckles in the upper canopy (Fig 1 & 2). Plants typically outgrow this damage. Prolonged hot weather during flowering may cause blossoms and small pods to abort.

Figure 1. Leaves of a bean plant with speckles from ozone damage

Brassica Crops –The conditions have also been favourable recently for Alternaria and Sclerotinia white rot. Sclerotinia will start as white mycelial growth followed by small, black spots/spores that look like mouse droppings within the fluffy white growth. These black spores can overwinter in the soil for up to 8 years and the best preventative management strategy is to rotate with non-susceptible crops such as beets, onions, spinach, corn, cereals or grasses. Once the crop is harvested, incorporate residue as soon as possible to reduce inoculum for future years. Managing chewing insects will also reduce the spread of Sclerotinia.

Carrots – Now is an important time to manage for Aster leafhoppers to prevent aster yellows. Ensure you’re monitoring your fields for activity and timing applications to peak counts. Historically Ontario aster yellows pressure mirrors Michigan and Michigan’s infectivity counts have been high for 2025.

Cucurbits – downy mildew is now present in all of the main pickling cucumber growing areas in Ontario. Infection levels range from 1-15%, depending on the field. Weekly preventative fungicides are required to prevent further infection and crop losses. Spore trapping results from Michigan are still detecting only clade 2 which impacts cucumber and cantaloupe crops.

Garlic – Harvest has started across the province. Remove bulbs from direct sunlight as soon as possible and be mindful of how long garlic is sitting in wagons/crates when there is no forced air present. Remove excess moisture from the crop as soon as possible as a slow cure will make it easy for pathogens to colonize wounds / bruises from harvest which will lower quality and the length of time the crop can be kept in storage. Be vigilant about reducing mechanical injury during harvest. When curing, controlling humidity is the most important variable to control. Curing over a long period of time (eg. 14+ days), can allow storage pathogens and bulb mites to acclimatize and cause problems in storage. Curing under a week is less favourable for pests and should allow the crop to be stored longer. The higher the quality of crop that goes into storage, the longer it will last.

Onions – Most fields are showing some Stemphylium lesions by now. Allegro 500F (group 29) is now registered for suppression of Stemphylium, Botrytis leaf blight and purple blotch on dry bulb onions. A product containing mancozeb (group M3s, such as Manzate Pro-Stick, Dithane Rainshield, and Penncozeb 75 DF Raincoat) may provide protection against Stemphylium if it is being applied to manage onion smut, Botrytis or Alternaria/Purple Blotch. Allego 500F and products containing a group 7 show the best efficacy, such as Sercadis, Aprovia, or Miravis Duo (group 7/3). Avoid applying products from the same chemical group one after the other to manage Stemphylium. Research has shown that there is very high resistance in Stemphylium to one of the fungicides in Quadris Top (group 11/3) and in Luna Tranquility (group 7/9). Levels of thrips are climbing in some fields. Apply no more than two consecutive insecticides from the same IRAC crop as thrips have a relatively short life cycle with multiple generations through the summer months and are at a high risk of developing insecticide resistance. The next generation of onion maggot and seedcorn maggot are active in many areas across the province. Be on the lookout for onion downy mildew and stunted/wilted plants due to onion maggot over the next week.

Potatoes – As mentioned in the Late Blight Update, late blight has been confirmed on potatoes in Dufferin County. Samples have been submitted for strain ID and results will be shared when available. The late blight strain the last few years has been US-23 which is susceptible to Ridomil. Although we’ve had hot weather recently, the high humidity, regular thunderstorms and irrigation means the risk of late blight remains high. If you haven’t recently applied a late blight specific fungicide, you should do so now. Visit the Ontario Crop Protection Hub to view registered late blight specific products on potatoes. Review the potato late blight entry in Ontario CropIPM to refresh yourself on what late blight infection looks like (Fig 3-7).

Figures 3 – 7. Late blight infected potato plants.

Because of the hot weather, insect development has sped up. Colorado Potato Beetle larvae are still being found in fields. Ensure you are rotating your foliar insecticides to delay resistance. Other insects such as potato leafhoppers, tarnished plant bugs and flea beetles have also been seen.

Sweet Corn – looking at the weather patterns over the last few weeks there have been a few opportunities for corn earworm migration into the area. So far this season the website insectforecast.com has been classifying the risk in the Great Lakes region as low. However we are hearing scattered reports of earworm in both sweet corn and tomatoes.

Sweet corn is attractive to the moths during the silking stage. Insecticide applications should be targeted towards the ears for optimum control. The corn earworm population has developed resistance to the pyrethroid (group 3A) insecticides. Group 28 products are effective, but more than one application may be necessary if the risk in this area increases. The Great Lakes and Maritimes Pest Monitoring Network is not currently reporting any trap catches in this region.

Manganese deficiency causes yellowing on the leaf tissue between the veins, creating a distinct pin-stripe pattern (Fig. 8 & 9). It often appears in the new growth first and is more commonly found on sandy soils, eroded knolls or areas with a high pH. Foliar applications of manganese sulfate can be used to prevent or correct deficiencies. Routine soil testing is the best way to identify manganese deficient soils.

Figure 8 – Corn leaf with pin-stripe pattern.

Pest Degree Day Forecasting

County	Carrot Rust Fly	Onion Maggot	Carrot Weevil	Aster Leafhopper	Tarnished Plant Bug	Cabbage Maggot	Seedcorn Maggot	European Corn Borer
THRESHOLD	329-395, 1399-1711	210-700, 1025-1515	138-156, 455+	128+	40+	314-398, 847-960, 1446-1604	200-350, 600-750, 1000-1150	See legend below
Bruce***	1099	995	710	550	348	799	995	478
Chatham-Kent*	1405	1286	957	770	529	1059	1286	684
Durham***	1262	1155	861	683	460	956	1155	602
Essex*	1506	1386	1050	851	590	1157	1386	760
Huron***	1228	1118	821	653	441	914	1118	579
Kemptville***	1281	1176	879	703	484	974	1176	626
Lambton**	1352	1234	915	732	503	1016	1234	651
Middlesex**	1376	1262	943	753	517	1044	1262	669
Norfolk**	1325	1211	891	706	480	992	1211	624
Peterborough	1185	1079	786	618	407	879	1079	543
Renfrew	1262	1159	867	697	484	961	1159	620
Simcoe***	1208	1101	813	644	437	904	1101	570
Sudbury***	948	862	622	486	310	697	862	425
Thunder Bay	823	740	514	379	209	584	740	318
Timiskaming***	930	844	612	479	302	685	844	416
Wellington Centre**	1196	1089	794	623	413	888	1089	548
Wellington North**	1200	1094	798	636	425	892	1094	563